The present invention relates to low molecular weight polymers.
In recent years there has been much research effort devoted to the preparation of low molecular weight polymers which can be utilized to prepare high solids coating compositions with a low volatile organic content. The thought has been, largely, that the lower the molecular weight of the polymer, the easier it would be to make low volatile organic content compositions. However, film properties such as hardness and durability often decrease as the molecular weight of the polymeric film-former decreases. This has been attributed to the average functionality of the polymer (number average molecular weight divided by equivalent weight) and the fact that polymers with lower levels of functionality tend to give softer films. One explanation which has been advanced concerns the level of non-functional polymer present. It has been generally thought that at least two functional groups must be present on each polymer backbone in order for the polymer to crosslink into the film. Therefore, low molecular weight polymers with less than two functional groups cannot contribute to the crosslinking network and thus tend to give poor film properties. There is a need, therefore, for a way to prepare polymers which have not only low molecular weight but which also have sufficient functionality in order to achieve good film properties.